Current visual display devices such as televisions typically employ cathode ray tubes ("CRTs"). Most televisions are driven by an analog video signal, which in North America, is governed by the NTSC standard. The standard NTSC signal, and other standard television signals, include both video and synchronizing ("sync") signals. In a color television signal, the video signals include luminance (e.g., intensity) and chrominance (e.g., color) information. The sync signal includes horizontal and vertical synching pulses, and horizontal and vertical blanking intervals. The horizontal synching pulses synchronize the horizontal sweep of the CRT's scanning electron gun with the source that produced the NTSC signal. Similarly, the vertical synching pulses synchronize fields or frames of displayed information on the CRT.
The horizontal blanking interval is a period that compensates for the time required for the electron gun to return from the right-hand side back to the left-hand side of the screen between the display of adjacent lines on the CRT. Likewise, the vertical blanking interval is a period that compensates for the time required for the electron gun to return from the bottom to the top of the screen between the display of consecutive frames. Well-known circuitry coupled to the CRT synchronizes and drives the electron gun in response to the video and synchronizing signals of the television signal to produce a coherent picture.
CRTs, however, are bulky, heavy, and consume significant amounts of power. Therefore, alternative displays have been developed such as liquid crystal displays ("LCDs") and electroluminescent displays. Such displays are typically referred to as "matrix displays" because they include an M row by N column matrix of display cells or "pixels".
In active matrix displays, such as LCDs, each display cell includes at least one switch, driven by a pointer signal, that enables the video signal to drive the display cell in the LCD. LCDs, for example, can employ one million pixels arranged in one thousand rows by one thousand columns. Therefore, many thousands of pointer signals are required to address each display cell in such an LCD.
Unfortunately, LCDs require thousands of interconnections between the display cells and external circuitry that provide the pointer signals. Since LCDs typically cannot be manufactured using standard integrated circuit packaging techniques, such displays are expensive to manufacture due to the thousands of interconnections required. While the manufacture of LCDs has recently become more economical, such displays are, however, still slow and dim compared to CRTs. Electroluminescent displays are quicker and brighter than LCDs, but are considerably more expensive to manufacture.
As noted above, individual display cells in the matrix are individually addressed by means of pointer signals. Typically, a given row is first addressed by a row pointer signal, and then each column is serially addressed by column pointer signals as luminance and chrominance data is provided to each display cell in the row. Such row and column addressing of display cells in the matrix display is similar to the addressing of memory cells in a semiconductor memory device. Therefore, typical computer generated signals are readily adapted for addressing and providing video signals to matrix displays. Matrix displays, however, cannot readily receive television signals such as standard NTSC television signals. Auxiliary circuitry is required to convert the horizontal and vertical synching pulses into clocking and addressing signals for addressing and writing data to each display cell in the matrix array.
If LCDs could be efficiently manufactured using standard integrated circuit manufacturing techniques, then it would be economical to monolithically integrate the LCD onto a single substrate with the auxiliary circuitry or synchronizing and clocking circuitry necessary for converting an NTSC signal into a signal appropriate for addressing the LCD. In addition to the difficulty in manufacturing LCDs under standard integrated circuit manufacturing techniques, however, conventional synchronization and clocking circuitry requires considerable area on a semiconductor substrate and consumes excessive power. Therefore, if manufacturing techniques improve, such circuitry could not likely be integrated with an LCD or other matrix displays on a single substrate. In addition to consuming significant area on a semiconductor substrate, typical synchronizing and clocking circuitry employed by televisions is complex. Therefore, such synchronizing and clocking circuitry would increase the complexity, and therefore the cost, of the LCD or other matrix display.